Project: Battery Showdown

Welcome to BitBox's Battery Showdown

To help demystify the tricky job of battery buying, we tasked our BitBox electronics design team with testing everyday AA cells.

But are cells that different? Yes. We were out of gas in just 5 minutes with one cell... Another gave 3 solid hours at high drain. Into toys, robots? LEDs? Digital cameras? Or bulk-buying for XBox360 games (thanks for the feedback!) ..these tests helped us buy AA's wisely.

We tested alkaline, lithium and zinc-chloride AA's to find the best AA batteries you can buy for your money on the highstreet and online. As far as we are aware, this is the largest scale discharge test of consumer batteries that has been performed. We tested more than 40 individual types of batteries in two discharge modes. Try sliding our 'outage' slider to choose your top AA. The results surprised us...

We are presenting a factual survey of batteries. The selection of batteries is not exhaustive and we have not deliberately included or excluded any brands or manufacturers. We are not recommending any manufacturer or brand based on these results and leave this up to the reader to decide which to buy. You can use the education resources here to learn how to choose wisely.

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Now for the facts. Unlike previous tests using various digital devices (such as cameras), toys or torches, we decided to do a methodical test by using a constant-current discharge load, built by ourselves. This allowed us to measure the exact stored energy in the battery, instead of using vague terms such as "45% more pictures" or "five times longer lasting". There are low-drain results, for things like toys, torches, CD/MP3 players and similar devices, and high drain results for devices like digital cameras. Click a button below to view one result set. We recommend looking at both data sets to get an idea of which the best overall battery would be for your own purposes.

Testing Methodology

The picture on the right shows the testing jig that was designed, tested, programmed and manufactured for this project (click for larger image.) Five analysers were built so multiple batteries could be tested simultaneously. We tested over 40 different batteries with prices per battery ranging from £0.08 to £1.13.

Batteries were purchased from discount shops (Poundland, 99p Stores, TJ Morris/Home Bargains, Poundworld and others), supermarkets (Tesco, Morrisons, Sainsbury's, Asda), retailers (Marks & Spencer, Wilkinsons, WH Smith, Superdrug, Tiger Direct, Maplin, Ikea, Whiz, and more) and online from a variety of suppliers. We also received a generous contribution of batteries from a Romanian reader. All batteries were new in retail packaging with expiration dates well into the future. We tried to test known brands, along with many unknown brands, to gather a wide data set.

Two discharges were performed: one at 200mA, which takes between 3 hours and 15 hours to complete, dependent on the chemistry. And one high-discharge current of 1000mA, which takes between 5 minutes and 3 hours, also depending on chemistry. We show nominal figures at 0.8V cut-off (due to this being the standard used in Energizer datasheets, among others), but data is also available for other discharge depths up to 1.35V. We used ARM Cortex™-M4 based STM32 datalogger to record several energy accumulations: mAh (milliampere·hours), mWh (milliwatt·hours) and joules. In addition, voltage, current, power and effective load resistance were logged.

All these are recorded on a laptop which connects to all analysers simultaneously using a Python application. At the end of the discharge, reports are generated, which are converted into graphs. All analysers were calibrated to within ±2% for the 200mA tests and ±3% for the 1000mA tests.

BitBox have released the analyser design as public domain. It may be downloaded here; this includes the Python application, firmware binary, schematics and PCB layout.

mAh vs mWh – the difference

The majority of batteries which have a rating (such as rechargeables) are rated in milliamp-hours, or mAh. 1000 mAh represents the equivalent energy load of 1000 milliamps applied for one hour. However, the issue with mAh is it fails to account for falling battery voltage. In general, a digital camera will use a switching converter, which will get more life with a higher mWh battery. But a torch, toy or similar device is fairly independent of voltage, and will last longer with a higher mAh battery. We provide both in the results tables so they can be compared.

About our industrial electronics design, prototyping and manufacturing services - BitBox Ltd is expert in designing electronics for today's products - in industry and professional applications of all kinds. Accurate power measurement, battery management and energy monitoring and control are a few of our core strenghts our many clients rely on. We supply streams of UK designed and manufactured products into live systems, operating 24/7 across the UK and beyond. These products are performing vital duties like saving our country's energy resources, reducing the cost of maintaining industrial plant and scanning life-critical data from valuable medical assets.

If you have a requirement to update or design a reliable electronic product and you need a local design and production partner who will make sure you product can be successful, please contact BitBox Ltd.

Suggestion for our next Showdown? Or, have a go at our #Gadget competitions!... Winners get a free BitBox Gadget delivered to your door. For these, please be sure to contact us via www.facebook.com/BitboxLtd here: BitBox Ltd. official facebook site .